Borrelia burgdorferi (sensu lato) encompasses several Borrelia species believed to be the causative agent of Lyme borreliosis (Lyme disease) including: B. burgdorferi sensu strict; B. garinii; and B. afzelii. Lyme disease is transmitted by the bite of various species of Ixodes ticks carrying the spirochete. The main reservoir of the infection in the United States is the white footed mouse, Peromyscus leucopus, and the infection can be transmitted to many mammalian species including dogs, cats, and man. (J. G. Donahue, et al, Am. J. Trop. Med. Hyg., 36:92-96 (1987); R. T. Green, et al, J. Clin. Micro., 26:648-653 (1988)).
Amblyomma americanum (Linnaeus), the lone star tick, is the primary vector of Ehrlichia chaffeensis, the bacterial agent of human monocytic ehrlichiosis (Anderson et al., 1993). In addition to Ehrlichia chaffeensis this aggressive human-biting tick species is also thought to vector other potential pathogens including Ehrlichia ewingii, Rickettsia rickettsii, R. amblyominii, Borrelia lonestari, Francisella tularensis and Coxiella burnetii (Calhoun, 1954; Burgdorfer, 1975; Barbour et al., 1996; Murphy et al., 1998; Burkot et al., 2001; Childs & Paddock, 2003). While Amblyomma americanum is found throughout geographical regions with a high occurrence of Lyme disease (Bishopp & Trembley, 1945; Anderson & Magnarelli, 1980; Hair & Bowman, 1986; Ginsberg et al., 1991; Luckhart et al., 1991; Keirans & Lacombe, 1998), there is no evidence that A. americanum transmits B. burgdorferi (Piesman & Happ, 1997). Reasons explaining why A. americanum fails to act as a suitable vector for B. burgdorferi have remained elusive.
Generally, arthropod vector refractoriness to a pathogen can be classified into three categories: (1) a lack of acquisition; (2) an inability to maintain growth of the pathogen; or (3) an inability to transmit the pathogen. In controlled experimental studies, as many as 25% of A. americanum larvae acquired spirochetes during infectious feedings. However, nearly all of these larvae were spirochete-negative before moulting to the nymphal stage (Piesman & Sinsky, 1988; Mather & Mather, 1990; Ryder et al., 1992; Piesman & Happ, 1997). Indeed, the refractory nature of A. americanum to maintaining and transmitting spirochetes has been previously recognized. Only one report of trans-stadial maintenance of infection in A. americanum nymphs has been published (Ryder et al., 1992), and one report of spirochete isolates from three pools of A. americanum adults (Teltow et al., 1991). However, these studies predate the discovery of the spirochete B. lonestari, or used methods that would not be able to discriminate between the two spirochete species, B. burgdorferi and B. lonestari (Barbour et al., 1996). Importantly, there has been no successful reported transmission of B. burgdorferi between infected and naïve hosts by A. americanum (Mukolwe et al., 1992; Ryder et al., 1992; Oliver et al., 1993; Sanders & Oliver, 1995; Piesman & Happ, 1997).
During A. americanum, I. scapularis and other Ixodid tick feeding, saliva is continuously secreted into the host (McMullen & Sauer, 1978; Coons et al., 1986; Sonenshine, 1991). A possible mechanism regulating transfer of B. burgdorferi has been previously identified as a factor in the saliva of A. americanum. (Ledin, K. E., et al., Med. Vet. Entomol., 2005; 19(1):90-95. However, specific molecules responsible for preventing transmission of B. burgdorferi during tick feeding are unknown making design and implementation of therapeutic methods and reagents difficult. Thus, there exists a need for identification of agents capable of controlling infection, growth, and viability of B. burgdorferi. 